The present invention relates to heating and cooling apparatus, and more particularly to a geothermal heat exchanger subcircuit for use with a conventional air conditioning unit.
Geothermal heating and cooling systems continue to grow in popularity. Geothermal systems are generally more efficient than conventional heating and cooling systems because they abstract from or release heat into a geothermal heat sink, such as the ground, a lake, a river, or a water well. Geothermal systems can typically be operated in either a heating mode or a cooling mode. In the heating mode, the geothermal heat exchanger draws heat from a geothermal heat sink and releases it into the indoor air. In the cooling mode, the geothermal heat exchanger draws heat from the indoor air and releases it into the geothermal heat sink. The efficiency of the geothermal system will depend in large part on the design of the heat exchanger and the temperature difference between the indoor air and the geothermal heat sink.
Air conditioning units are widely used throughout the United States to provide cooling of indoor air. A conventional air conditioning system 110 is shown in FIG. 3, and includes an outdoor unit 112 having an outdoor housing 140 that contains a compressor 118 for circulating refrigerant through the system, an accumulator 122 for handling certain refrigerant imbalances within the system, an outdoor coil 132 for exchanging heat with the outdoor air, and a fan 128 for moving air across the coil 132. A conventional system 110 also includes an indoor unit 114 having an indoor housing 138 that contains an indoor coil 132 for exchanging heat from the indoor air and a fan 136 for moving air across the indoor coil 132. The indoor and outdoor units, 114 and 112 respectively, are interconnected by refrigerant lines 148 and 146. Air conditioning units operate only to cool indoor air, and are typically shut-off when cooling is not desired. In operation, the air conditioning unit circulates refrigerant through the indoor coil 132 and the outdoor coil 120. The refrigerant draws heat from the indoor air as it evaporates in the indoor coil 132 and release the heat it into the outdoor air as it condenses in the outdoor coil 120.
A number of attempts have been made to combine the components of a geothermal system with the components of an air conditioning unit. For example, U.S. Pat. No. 5,461,876 issued Oct. 31, 1995 to Dressier discloses a system having a ground loop with a direct earth heat exchanger and an air loop with an outdoor air coil. The Dressler system is designed to permit the air loop and ground loop to operate individually, serially or in parallel to provide either heating or cooling as desired. The Dressler system is specially designed from the ground up to replace existing air conditioning units and geothermal systems. As a result, the Dressler system requires significant custom assembly. In addition, the Dressler system requires a large supply of refrigerant to fill both the outdoor air coil and the direct earth heat exchanger when the two components operate in series.